Creating Hive replication policy

Before you create a Hive replication policy, you must ensure that the required Ranger policy is set in Ranger.

  1. On the Management Console > Replication Manager > Replication Policies page, click Add Policy.
    The Create Replication Policy wizard appears.
  2. On the General page, choose or enter the following information:
    Option Description
    Hive Creates a Hive replication policy.
    Policy Name Enter a unique name for the replication policy.
    Description Optional. Enter a brief description about the replication policy.

    The following image shows a sample General page in the Create Replication Policy wizard:

  3. Click Next.
  4. On the Select Source page, enter or choose the options as required:
    Option Description
    Source Databases and Tables Enter the database name and table name. Click Add to enter more databases and tables as necessary.
    Source User Enter the username. Ensure that the user has the necessary permissions to replicate data.
  5. Click Next.
  6. On the Select Destination page, enter or choose the options as required:
    Option Description
    Destination Data Lake The Managed Warehouse Path and the Hive External Table Base Directory Path for the Data Lake appears.
    Cloud Credential on Source Choose the required cloud credential. The cloud credentials that you register for the selected source cluster on the Cloud Credentials page appear in this field. You can also add cloud credentials using the Add Cloud Credential link.
    Run as Username Enter the source cluster user name.
  7. Click Validate Policy.
    Replication Manager verifies whether the details provided are correct.
  8. Click Next.
  9. On the Schedule page, choose or enter the following information:
    Option Description
    Run Now Starts to replicate the existing HDFS data after the replication policy creation is complete. Choose the frequency to replicate data periodically.
    Schedule Run Runs the replication policy to replicate data at a later time. Choose the date and time for the first run, and then choose the frequency to replicate data periodically.
    Frequency

    Choose one of the following options:

    • Does Not Repeat
    • Custom - In the Custom Recurrence dialog box, choose the time, date, and the frequency to run the policy.
  10. Click Next.
  11. On the Additional Settings page, enter or choose the values as necessary:
    Option Description
    YARN Queue Name Enter the name of the YARN queue for the cluster to which the replication job is submitted if you are using Capacity Scheduler queues to limit resource consumption. The default value for this field is default.
    Maximum Maps Slots Set the maximum number of map tasks (simultaneous copies) per replication job. The default value is 20.
    Maximum Bandwidth Adjust this setting so that each map task is throttled to consume only the specified bandwidth.

    Each map task ((simultaneous copy) is restricted to consume only the specified bandwidth. This is not always exact. The map throttles back its bandwidth consumption during a copy in such a way that the net bandwidth used tends towards the specified value. You can adjust this setting so that each map task is throttled to consume only the specified bandwidth so that the net bandwidth used tends towards the specified value. The default value for the bandwidth is 100MB per second for each mapper.

    Sentry Permissions Choose one of the following options:
    • Include Sentry Permissions with Metadata migrates Sentry permissions during the replication job.
    • Exclude Sentry Permissions from Metadata does not migrate Sentry permissions during the replication job.
    Skip URI Privileges Select this option if you do not want to include URI privileges when you migrate Sentry permissions.

    During migration, the URI privileges are translated to point to an equivalent location in S3. If the resources have a different location in Amazon S3, do not migrate the URI privileges because the URI privileges might not be valid.

    Replication Strategy Choose one of the following replication strategies to determine whether the file replication tasks should be distributed among the mappers statically or dynamically.
    • Static distributes file replication tasks among the mappers up front to achieve an uniform distribution based on the file sizes.
    • Dynamic distributes the file replication tasks in small sets to the mappers, and as each mapper completes its tasks, it dynamically acquires and processes the next unallocated set of tasks.
    The default replication strategy is Dynamic.
    MapReduce Service Choose the MapReduce or YARN service to use.
    Log Path Enter an alternate path for the logs, if required.
    Error Handling Select the following options as necessary:
    • Skip Checksum Checks - Determines whether to skip checksum checks on the copied files. If selected, checksums are not validated. Checksums are checked by default.
      Checksums are used for two purposes:
      • To skip replication of files that have already been copied. If Skip Checksum Checks is selected, the replication job skips copying a file if the file lengths and modification times are identical between the source and destination clusters. Otherwise, the job copies the file from the source to the destination.
      • To redundantly verify the integrity of data. However, checksums are not required to guarantee accurate transfers between clusters. HDFS data transfers are protected by checksums during transfer and storage hardware also uses checksums to ensure that data is accurately stored. These two mechanisms work together to validate the integrity of the copied data.
    • Skip Listing Checksum Checks - Whether to skip checksum check when comparing two files to determine whether they are same or not. If skipped, the file size and last modified time are used to determine if files are the same or not. Skipping the check improves performance during the mapper phase. Note that if you select the Skip Checksum Checks option, this check is also skipped.
    • Abort on Error - Whether to abort the job on an error. If selected, files copied up to that point remain on the destination, but no additional files are copied. Abort on Error is not selected by default.
    • Abort on Snapshot Diff Failures - If a snapshot diff fails during replication, the replication policy uses a complete copy to replicate data. If you select this option, the policy aborts the replication when it encounters an error instead.
    Preserve Choose the required options to preserve the block size, replication count, permissions (including ACLs), and extended attributes (XAttrs) as they exist on the source file system, or to use the settings as configured on the destination file system. By default source system settings are preserved.

    When Permission is selected, and both the source and destination clusters support ACLs, replication preserves ACLs. Otherwise, ACLs are not replicated. When Extended attributes is selected, and both the source and destination clusters support extended attributes, replication preserves them. (This option only displays when both source and destination clusters support extended attributes.)

    If you select one or more of the Preserve options and you are replicating to S3 or ADLS, the values all of these items are saved in metadata files on S3 or ADLS. When you replicate from S3 or ADLS to HDFS, you can select which of these options you want to preserve.

    Delete Policy Choose the required options to determine whether the files that were deleted on the source should also be deleted from the destination directory. This policy also determines the handling of files in the destination location that are unrelated to the source. Options include:
    • Keep Deleted Files - Retains the destination files even when they no longer exist at the source. This is the default option.
    • Delete to Trash - If the HDFS trash is enabled, files are moved to the trash folder. This is not supported when replicating to S3 or ADLS.
    • Delete Permanently - Uses the least amount of space; use with caution.
    Alerts Choose the required options to generate alerts for various state changes in the replication workflow. You can alert on failure, on start, on success, or when the replication workflow is aborted.
  12. Click Create.
After the replication policy runs successfully, you can view the replication job status on the Replication Policies page. Verify whether the job starts and runs as expected.

The administrator can verify whether the job starts and runs as expected using the following steps:

  • For HDFS data replication, check the cloud storage path (for example, S3 bucket path) to verify whether the data was successfully copied in the specified bucket.
  • For Hive metadata replication, verify whether the specified source database, along with tables, partitions, UDFs and column stats are available in the Data Lake HMS instance. For this, the administrator can use a Data Hub cluster and run the corresponding queries using Hue or beeline.
  • For Ranger policies, query the Ranger policies to ensure that the Sentry policies are properly mapped as Ranger policies for the right users and groups.